In order to reduce galvanic action and oxidation on pipe which is buried in the ground it is a practice to wrap pipe with a nonconductive impervious material. To facilitate wrapping the pipe machines have been developed which are positioned on the pipe, the machines including a spindle for receiving a roll of tape. As the machine is rotated around the pipe it automatically advances along the pipe. One end of the tape is affixed to the pipe and as the machine rotates around the pipe the tape is unwound from the spoon and wound onto the pipe. The tape is wound so that it overlaps to form a continuous covering around the pipe.
In order to properly affix the tape to the pipe, a certain amount of tension must be applied to the tape. The tension force required varies according to several factors, including the diameter of the pipe, the width of the tape, the type and thickness of the tape and so forth. If too little tension is applied on the tape as it is wound on the pipe it will not firmly seal against the pipe with the possibility of leaving air holes by which galvanic action may occur or contact of the pipe may be had with water or the earth, resulting in more rapid deterioration of the pipe. On the other hand, if the tension is too great, the tape will be stretched to a point where either the tape breaks, or the thickness of the tape applied to the pipe will be decreased so that the required thickness specifications are not obtained.
In order to maintain tension on the tape it has been a practice to apply a braking force on the spindle to which the roll of tape is supported so as to resist the unrolling of the tape as the machine rotates around the pipe. If the diameter of the roll of tape remains constant such arrangement would be completely satisfactory. Since the diameter of a roll of tape constantly changes as the tape is applied to the pipe, starting out with the full diameter of the roll of tape as it is placed on the spindle and decreases to the minimum diameter of the tape spool as the last portion of the tape is used, a preselected fixed amount of tension against the rotation of the spindle on which the tape roll is positioned results in an uneven amount of tension being applied to the tape. It can be seen that the moment arm of a full roll of tape is much greater than that of a near empty roll of tape. Therefore, with fixed friction on the spindle, much more tension is supplied to the tape when the spool is nearly empty than is applied when a full spool is first placed on the spindle.
It is therefore an object of this invention to provide a machine for wrapping tape on a pipe including improved means of controlling the tension on the tape.
More particularly an object of this invention is to provide a machine for wrapping tape on a pipe including means of controllably varying the tension applied to resist the rotation of the spool on which the tape is placed, the tension being varied so that it is proportional to the diameter of the roll of tape on the spindle so that thereby the tension applied to the tape remains relatively constant as the tape is removed from the roll.
These general objects, as well as other and more specific objects of the invention will be fulfilled in the the following description and claims, taken in conjunction with the attached drawings.